You usually need a fixed address and residence permit to open an account. Many banks require inkan, but the major banks also offered accounts (i.e. people could use their signature as authority other than the inkan), primarily aimed at foreigners. Or, at least Sumitomo Bank used to, I don't know if they still do.
You should be able to rent a mobile phone at the airport. Maybe there are other options, but I think without an address your options will be very limited.